The present invention relates to the field of perfumery. It relates, more particularly, to perfuming compositions or perfumed products containing a class of aliphatic or aromatic keto esters of fragrant alcohols, as defined below, which are capable of releasing said fragrant alcohol upon exposure to light, more particularly daylight. The present invention also relates to xcex1-keto esters, as defined below, of alcohols which are precursors of fragrant aldehydes and ketones and which are capable of releasing said fragrant ketone or aldehyde upon exposure to light, more particularly daylight. Said xcex1-keto esters may furthermore contain, in xcex1-position to the keto group, an alkyl group which may contain various substituents and which alkyl group is derived from a fragrant molecule possessing an olefinic unsaturation. The unsaturated molecule and/or the aldehyde or ketone are released upon exposure to light, in particular daylight, of the xcex1-keto ester.
There exists, in perfumery, a particular interest in compounds which are capable of xe2x80x9cfixingxe2x80x9d fragrant molecules, for example by chemical bonding or intramolecular forces like absorption, and releasing said fragrant molecules over a prolonged period of time, for example by the action of heat, enzymes, or even sunlight. Fragrant molecules have to be volatile in order to be perceived. Although many fragrant compounds are known to have good substantivity, i.e. they will cling to a surface to which they have been applied for several days and can hence be perceived over such a period of time, a great number of fragrant compounds are very volatile, and their characteristic smell can no longer be perceived after one or two days or even after several hours.
It is thus desirable to dispose of fragrance delivery systems which are capable of releasing the fragrant compound or compounds in a controlled manner, maintaining a desired smell over a prolonged period of time.
We have now developed a fragrance delivery system which is capable of releasing fragrant alcohols upon exposure to light, and in particular daylight. One object of the present invention is a delivery system which comprises 2-benzoyl benzoates and 2-alkanoyl benzoates of formulae 
in which
R1 represents hydrogen or a group of formula 
xe2x80x83in which X and Y can be identical or different and represent, independently from each other, hydrogen, a linear or branched alkyl or alkoxy group from C1 to C12, a phenyl group which is optionally substituted, an olefinic group from C2 to C12, an alcohol group, a CO2M group, a xe2x80x94NR6R7 group or a group of formula 
R2 can be identical to R1 or different from it and represents hydrogen, a linear or branched alkyl or alkoxy group from C1 to C12, a phenyl group which is optionally substituted, an olefinic group from C2 to C12, an alcohol group, a CO2M group, a xe2x80x94NR6R7 group, a group of formula 
xe2x80x83or a polyalcohol or polyether group;
R3 represents hydrogen, an alkyl or alkoxy group from C1 to C4, linear or branched, a OH group or a NH2 group;
R4 and R5, taken separately, have the meaning given above for R1 and can be identical to or different from R1 or from each other; or
R4 and R5, taken together, form a bridging group between the two aromatic rings, which bridging group can be a methylene or a keto group;
m is an integer from 0 to 3 and n is an integer from 0 to 2; R6 and R7, taken separately, each represents hydrogen, an alkyl group from C1 to C4, an alcohol group having an alkyl chain from C1 to C12, or a phenyl group, or, R6 and R7, taken together with the nitrogen atom form a 5-membered or six-membered ring possibly containing another hetero atom;
R8 represents hydrogen, an alkyl group from C1 to C4, an alcohol group having an alkyl chain from C1 to C12 or a phenyl group;
M represents hydrogen or an alkali metal; and
R* is the organic part derived from a primary or secondary fragrant alcohol R* OH.
In the above definition, when reference is made to a fragrant alcohol, there is always meant an alcohol which not only has an odor, but which is also known to a person skilled in the art as being useful as perfuming ingredient for the formulation of perfumes or perfumed articles. The criteria a useful perfuming ingredient has to fulfil are known to a person skilled in the art and include, amongst others, a certain originality of the odoriferous note, stability and a certain price/performance ratio. Non-limiting examples for fragrant alcohols which can be used with the benzoates of the invention will be mentioned below.
The advantage of the fragrance delivery system of the present invention lies in its capacity to slowly release the fragrant alcohols R*OH from which the benzoyl benzoate esters of formula (I) or the alkanoyl benzoate esters of formula (II) are derived. The release occurs when said esters are exposed to daylight in particular. Upon absorption of energy from said light, the ester undergoes a photoreaction in the course of which the fragrant alcohol is released from the molecule into the surroundings. Said release occurs in a controlled manner, i.e. a more or less constant amount of alcohol R*OH is formed over a period of time, without an initial burst of very intense odor which becomes rapidly imperceptible as is the case with volatile alcohols. Because the release of the alcohol R*OH can occur over several days or weeks, the use of the system of the present invention obviates the drawbacks of many fragrant alcohols R*OH which are of pleasant smell but also very volatile. Good examples are citronellol and geraniol which can only be perceived over a short period of, say, one or two hours, when applied to the surface of, for example, tiles and windows in the course of a cleaning procedure using liquid cleaners; even in solution, the typical smell of said alcohols disappears within several hours. It goes without saying that the concentration of the alcohols in the application plays an important role in the time during which the fragrant molecules can be perceived.
With the system of the present invention, the typical odor of the alcohol R*OH is perceived over a much more prolonged period of time, as the 2-benzoyl benzoate or the 2-alkanoyl benzoate of the fragrance delivery system, which are not volatile, remain on the surface to which they are applied or in the solution into which they are incorporated. Upon exposure to light, the fragrant alcohol R*OH is released, and it is clear that this reaction can provide perceptible amounts of the alcohol over days or weeks, depending, amongst others, on the amount or the concentration of the fragrance delivery system, the time of exposure to light, its intensity and its wavelength.
2-Benzoyl benzoate esters of the above formula (I) which can carry various substituents in positions R1, R2, R3, R4 and R5 are known to be photolabile compounds. It was suggested to use these esters as protective groups for alcohols in organic synthesis and subsequently release the alcohol present in the ester function by photolysis (see Porter et al., J. Org. Chem 1996, 61, 9455-9461). The authors conducted experiments with different alcohols, and they described the elimination of geraniol from the geranyl 2-benzoyl benzoate (R1xe2x95x90R2xe2x95x90R3xe2x95x90R4xe2x95x90R5xe2x95x90H). However, it has not been described or suggested to use the said esters in perfumery, as a fragrance delivery system which is capable of releasing the fragrant alcohol over a prolonged period of time and thus provide a slow release fragrance effect.
As fragrant alcohol R*OH derived radical R* in the above formula (I), in principle a group derived from any fragrant alcohol which is known in the art can be used. Primary and secondary alcohols are shown to be useful in the present invention as they are liberated when exposed to daylight.
As non-limiting examples of alcohols which can be used in the present invention in the form of the 2-benzoyl benzoate esters, one can cite anisic alcohol, cinnamic alcohol, fenchylic alcohol, 9-decen-1-ol, phenethylol, citronellol, 3-methyl-5-phenyl-1-pentanol (origin: Firmenich SA, Geneva, Switzerland), Mayol(copyright) (7-p-menthan-1-ol ; origin: Firmenich SA, Geneva, Switzerland), geraniol (3,7-dimethyl-2,6-octadien-1-ol), (Z)-3-hexen-1-ol, 1-hexanol, 2-hexanol, 5-ethyl-2-nonanol, 2,6-nonadien-1-ol, borneol, 1-octen-3-ol, cyclomethyl citronellol, decanol, dihydroeugenol, 8-p-menthanol, 3,7-dimethyl-1-octanol, dodecanol, eugenol, isoeugenol, Tarragol(copyright) (2-methoxy-4-propyl-1-cylohexanol; origin: Firmenich SA, Geneva, Switzerland), Polysantol(copyright) [(E)-3,3-dimethyl-5-(2xe2x80x2,2xe2x80x2,3xe2x80x2-trimethyl-3xe2x80x2-cyclopenten-1xe2x80x2-yl)-4-penten-2-ol; origin: Firmenich SA, Geneva, Switzerland] and Limbanol(copyright) [1-(2xe2x80x2,2xe2x80x2,3xe2x80x2,6xe2x80x2-tetramethyl-cyclohex-1-yl)-3-hexanol ; origin: Firmenich SA, Geneva, Switzerland].
It is quite obvious, however, that the process of the invention is perfectly general and can relate to many other alcohols which the skilled person is quite able to choose from the general knowledge in the art and as a function of the olfactive effect it is desired to achieve. The above list therefore is more illustrative for fragrant alcohols which are known to a person skilled in the art, and whose delivery can be improved, but it is clearly quite impossible to cite in an exhaustive manner all alcohols of formula R*OH which have a pleasant odor and the 2-benzoyl or 2-alkanoyl benzoate esters of which can be used in the fragrance delivery system of the present invention.
From the foregoing, it is evident that the fragrance delivery system is particularly appropriate for delivering fragrant alcohols R*OH which are very volatile, or which have a low perception threshold, like geraniol, citronellol or phenethylol. The benzoyl and alkanoyl benzoate esters (I) of the latter are thus preferred according to the present invention.
The chemical reaction which releases the fragrant alcohol can only occur when a source of a hydrogen radical Hxe2x80xa2 is present in the fragrant delivery system. Said hydrogen radical is transferred to the oxygen of the keto-function, causing it to become reduced. Such a source can be intramolecular, i.e. the hydrogen radical comes from the 2-benzoyl benzoates of formula (I) or the 2-alkanoyl benzoates of formula (II) themselves, or intermolecular, i.e. the hydrogen radical comes from another, different source which is present in the medium in which the ester is incorporated. The intramolecular pathway or mechanism is a universal mechanism which can occur in every possible application medium, thus in the liquid or solid state. The intermolecular mechanism, however, is only possible in solution, but not in the solid state. Examples of liquid state application media are liquid air-fresheners which release the fragrant alcohol upon exposure to light. Examples of release of the fragrant alcohol in the solid state are surfaces, like those of tiles or windows, which are cleaned with a cleaner containing the fragrance delivery system of the invention, the system being thus deposited on the surface after cleaning and remaining on it as a solid film after evaporation of the liquids present in the cleaner. However, it has to be understood that the term xe2x80x9csolidxe2x80x9d as used beforehand is used to designate the benzoates in the neat state in which they may be a real solid, crystalline or non-crystalline, or be in the form of a more or less viscous oil.
For the 2-benzoyl benzoates of the above formula (I) or the 2-alkanoyl benzoates of the above formula (II) in which R1, R4 and R5 are hydrogen, an external hydrogen radical source is necessary. In general, the hydrogen radical will be abstracted from the solvent in which the 2-benzoyl or the 2-alkanoyl benzoate is dissolved or provided by a solvent which is added to the solution containing the said compound. Suitable sources are known to a person skilled in the art. The most important criterion a suitable hydrogen radical source has to fulfil is that a stable radical is formed after abstraction of the hydrogen. For a given compound, and independently from other functional groups or structural elements present in the same, the presence of hydrocarbon groups which are not methyl or tert-butyl is very favorable towards the formation of a stable radical after hydrogen abstraction. Suitable groups include ethyl or n-propyl. Even better are branched secondary alkyl groups, like isopropyl or sec-butyl. It is preferred when the solvent contains an isopropyl group or is a primary or secondary alcohol. Non-limiting examples for classes of solvents are the following: aliphatic and aromatic alcohols, like methanol, ethanol, propanol, decanol or benzyl alcohol, in particular isopropanol; diols and polyols, like ethyleneglycol, glycerol, polyethyleneglycol, propyleneglycol or polypropyleneglycol; ketones, such as diisopropylketone; esters, such as isopropylacetate; aromatic solvents, such as ethylbenzene, cyclohexylbenzene or isopropylbenzene (cumene), di- or triisopropylbenzene; ethers, such as diisopropylether, tetrahydrofuran, mono-, di- or triethyleneglycoldimethylether, diethyleneglycolmonoether or polyethyleneglycoldimethylether; aminoalcohols, such as mono-, di- or triethanolamine; hydrocarbons, in particular branched hydrocarbons, including limonene.
Preferred solvents include primary and secondary alcohols, in particular isopropanol, 1-dodecanol, 2-tridecanol, butanol or amyl alcohol.
All the above-mentioned solvents can, of course, also be used for benzoyl and alkanoyl benzoate esters which react in an intramolecular pathway to release the fragrant alcohol. In such case, R1, R4 or R5 are the intramolecular hydrogen radical source, as will be described below.
The mentioned solvents will be chosen according to their ability to release hydrogen radicals.
We have found that the intramolecular pathway for the release of the fragrant alcohol only occurs when at least one of the groups R1, R4 or R5 of formula (I) or (II), which is in 2-position relative to the keto function, is a group of formula 
from which the hydrogen radical is easily transferred to the keto function, due to the vicinity of the group R1 to the keto function by which an energetically favorable transition state is possible. X and Y are chosen to stabilize the resulting radical 
which remains after abstraction of the hydrogen radical and its transfer to the keto function. Suitable groups X and Y which can stabilize radicals are known to a person skilled in the art, and X and Y, which can be the same or different, will be chosen according to the respective benzoyl benzoate and the fragrant alcohol R*OH used in a given fragrance delivery system in order to give the best results, i.e. the desired release rate for the fragrant alcohol. Preferably X and Y are, independently from each other, a group as defined above with respect to formulae (I) and (II).
The compounds of formula (I) can contain, in addition to the substituent R1 in 2-position of the cycle relative to the keto function, a further substituent R4 in 6-position. It is evident that this substituent R4 can also function as a hydrogen radical source, after a rotation around the single bond between the keto function and the phenyl ring. Moreover, the same applies to the group R5 of the above formula (I) or (II), which is optionally present in the phenyl ring which carries the ester function. R5, after a rotation of the phenyl group, can also serve as a hydrogen radical source. R4 and R5 thus have the same meaning as R1, which has been defined above, and R4 and R5 can be identical to R1, or they can be different from R1 and, respectively, from each other.
The two phenyl groups of the 2-benzoyl benzoates or formula (I) can furthermore be bridged by a methylene or keto group.
We have furthermore found that it can be advantageous with respect to the release of the fragrant alcohol when the respective benzoyl benzoate of formula (I) or the respective alkanoyl benzoate of formula (II) carries a substituent R3 other than hydrogen in the ortho-position to the xe2x80x94COOR*xe2x80x94function. The purpose of this substituent is to establish a favorable conformation of the xe2x80x94COOR*xe2x80x94function relative to the keto group, or respectively to the reduced keto-group, in order to facilitate the cyclization to the lactone which occurs after release of the alcohol. This reaction leads to the release of the fragrant alcohol R*OH. Practically, any group which is inert towards the xe2x80x94COOR*xe2x80x94function can be used, and they are known to a person skilled in the art. The groups defined in the above formula (I) and (II), namely linear or branched alkyl or alkoxy from C1 to C4, OH or NH2 have revealed themselves as being appropriate from the point of view of effectiveness, and, of course, synthetic access.
The benzoyl benzoates of formula (I) and the alkanoyl benzoate of formula (II) can furthermore carry one or more substituents R2 in the positions indicated and defined above. Substituents R2, however, seem to be of less importance to the reactivity and the performance of the fragrance delivery system of the present invention, although it is often preferred, for reasons of easy accessibility of the corresponding 2-benzoyl and 2-alkanoyl benzoates of the invention, to use an ester wherein R2 is a group other than hydrogen. It is however possible to adapt e.g. the stability of the 2-benzoyl and 2-alkanoyl benzoates of the present invention to the respective application desired. The 2-benzoyl benzoates can e.g. be rendered more hydrophilic by one or more groups R2 which are a quaternary amine group, a polyalcohol group or a polyether group. Specific examples for said functional groups are known to a person skilled in the art, and the groups will be chosen according to the effect desired.
Preferred 2-benzoyl benzoate esters of the present invention are those of formula 
in which
R1 is a branched alkyl group from C3 to C4 containing a secondary hydrocarbon group;
R2 is a branched alkyl group from C3 to C4 and is identical to R1;
R3 is hydrogen or a linear or branched alkyl group from C1 to C4;
R4 is hydrogen or a linear or branched alkyl group from C1 to C4;
R5 is hydrogen or a linear or branched alkyl group from C1 to C4;
R* is the organic part derived from a primary or secondary fragrant alcohol R*OH.
Generally, with respect to the above formulae (I) and (Ixe2x80x2), it can be said that it is preferred when R1, R4 or R5 which are responsible for the transfer of the hydrogen radical towards the keto function, is an isopropyl group, irrespective of the other substituents which may be present in the molecule. The isopropyl group was found to be the substituent which is most easily available, from a synthetic point of view, and which readily transfers hydrogen to the keto function, which we attribute to its ability to form a stable radical after abstraction of hydrogen.
The most preferred compounds according to the above formula (Ixe2x80x2) are geranyl 2-(2xe2x80x2-isopropylbenzoyl)benzoate, geranyl 2-(2xe2x80x2,4xe2x80x2-diisopropyl-benzoyl)benzoate and 3,3-dimethyl-5-(2xe2x80x2,2xe2x80x2,3xe2x80x2-trimethyl-3xe2x80x2-cyclopenten-1xe2x80x2-yl)-4-penten-2-yl 2-(2xe2x80x2,4xe2x80x2-diisopropylbenzoyl)benzoate [(E)-3 ,3-dimethyl-5-(2xe2x80x2,2xe2x80x2,3xe2x80x2-trimethyl-3xe2x80x2-cyclopenten-1xe2x80x2-yl)-4-penten-2-ol is a secondary alcohol sold under the name Polysantol(copyright) by Firmenich SA, Geneva, Switzerland].
The 2-benzoyl and 2-alkanoyl benzoates of the present invention are synthesized by esterification of the respective 2-benzoyl and 2-alkanoyl benzoic acids with the desired alcohol, in a way known to a person skilled in the art, preferably using 4-dimethylaminopyridine in pyridine and 1,3-dicyclohexylcarbodiimide. The above-mentioned benzoic acids are obtained from the respective phthalic anhydride. This latter is brought to reaction, for example, with the desired substituted or unsubstituted benzene in a Friedel-Crafts reaction. If necessary, the respective phthalic anhydride can also be reacted with the Grignard reagent, the organolithium compound or another appropriate organometallic compound of the desired substituted or unsubstituted benzene or alkane, respectively.
A further object of the present invention is a fragrance delivery system comprising xcex1-keto esters of formula 
in which
Rxe2x80x2* is hydrogen or a linear or branched, unsubstituted or substituted alkyl group from C1 to C35, an unsubstituted or substituted cycloalkyl group from C5 to C6, an unsubstituted or substituted phenyl or naphthyl group, or an alkyl group carrying an abstractable hydrogen in xcex3-position relative to the xcex1-keto function and comprising a moiety from which is derived a fragrant compound containing an olefin function, such that said fragrant compound containing an olefin function is eliminated after abstraction of said xcex3-hydrogen atom;
Rxe2x80x3* is hydrogen or a methyl, ethyl or tert-butyl group or is the organic part of a primary or secondary alcohol from which is derived a fragrant aldehyde or ketone, at least one of the groups Rxe2x80x2* and Rxe2x80x3* being a group which is derived from a fragrant compound.
In the above definition, when reference is made to a fragrant compound, aldehyde or ketone, it is always meant a compound which not only has an odor, but which is also known to a person skilled in the art as being useful as a perfuming ingredient for the formulation of perfumes or perfumed articles. The criteria a useful perfuming ingredient has to fulfil are known to a person skilled in the art and include, amongst others, a certain originality of the odoriferous note, stability and a certain price/performance ratio. Non-limiting examples for fragrant compounds which can be used with the xcex1-keto esters of the invention will be mentioned below.
Like the above-described 2-benzoyl benzoates and 2-alkanoyl benzoates, the xcex1-keto esters of the above formula (III) release fragrant compounds upon exposure to light, in particular daylight. The xcex1-keto esters of formula (III), however, are capable of eliminating, i.e. releasing, either a fragrant compound containing an olefin function from the group Rxe2x80x2* in 1-position relative to the keto function, or a fragrant aldehyde or ketone which is derived from the alcohol Rxe2x80x3*OH from which the organic part Rxe2x80x3* is present in the ester function of the keto esters of the present invention.
The release of the fragrant compound from the keto esters occurs after an intramolecular transfer of an abstractable hydrogen radical, in xcex3-position to the xcex1-keto function, to said keto function. The respective part of the molecule from which the hydrogen radical has been abstracted is subsequently released from the reduced keto ester, with concomitant formation of a double bond. The above is illustrated in the scheme below in which possible substituents in the respective parts of the molecules have been omitted for reasons of clarity. The double bonds which will be formed after elimination are indicated by dotted lines. 
It is to be understood that the xcex1-keto esters of the present invention can release only one molecule of fragrant compound per molecule of xcex1-keto ester. However, when the hydrogen transfer to the xcex1-keto function is able to occur from the one or the other side of said function, as illustrated above, a certain part of the molecules will release a ketone or aldehyde and a certain part will release the olefin compound. The proportions of the two products released depend on the relative rate of each hydrogen transfer reaction. According to the effect desired, the xcex1-keto esters of the invention can be tailored to release exclusively a fragrant ketone or aldehyde, or exclusively a fragrant compound containing an olefin group, or both. When only one of the two classes of fragrant compounds is to be released from the xcex1-keto esters of the invention, the part of the molecule from which no release shall occur does not contain an abstractable hydrogen atom in xcex3-position to the keto function, i.e. either no hydrogen atom at all is present in the said position, or it is one which is not abstracted.
It is evident that a fragrance delivery system which contains the xcex1-keto esters of the above formula (III) has all the advantages described above for the 2-benzoyl and 2-alkanoyl benzoates of formula (1) and (II), i.e. the release of the fragrant compound occurs in a more or less constant amount. No initial burst of very intensive odor which becomes imperceptible after a relatively short period of time occurs, as is often observed with volatile aldehydes or ketones or fragrant compounds containing an olefin group. With the xcex1-keto esters of the present invention, such disadvantages are obviated because the esters will remain on a surface to which they have been applied or in the solution into which they have been incorporated. Upon exposure to light, the fragrant compound or compounds are released, and this reaction can provide perceptible amounts of the compound over days or weeks, depending, amongst others, on the amount or the concentration of the xcex1-keto esters, the time of exposure to light and its intensity.
Additionally, the xcex1-keto esters of the present invention allow for the generation of mixtures of two different fragrant compounds, and in different proportions, if desired.
In principle, any fragrant aldehyde or ketone which is known in the art can be released from the xcex1-keto esters of the invention in which they are chemically bound in the form of the ester of their corresponding secondary or primary alcohol.
Non-limiting examples for fragrant aldehydes which can be released from the xcex1-keto esters include saturated and unsaturated aldehydes from C6 to C13, citral, citronellal, campholenic aldehyde, cinnamic aldehyde, hexylcinnamic aldehyde, formyl pinane, hydroxycitronellal, cuminic aldehyde, vanillin, ethylvanillin, Lilial(copyright) [3-(4-tert-butylphenyl)-2-methylpropanal; origin: Givandan-Roure SA, Vernier, Switzerland], Lyral(copyright) [4- and 3-(4-hydroxy-4-methylpentyl)-3-cyclohexene-1-carbaldehyde; origin: International Flavors and Fragrances, USA], Bourgeonal(copyright) [3-(4-tert-butylphenyl)propanal; origin: Quest International, Naarden, Netherlands], heliopropanal [3-(1,3-benzodioxol-5-yl)-2-methylpropanal; origin: Firmenich SA, Geneva, Switzerland], Zestover (2,4-dimethyl-3-cyclohexene-1-carbaldehyde; origin: Firmenich SA, Geneva, Switzerland), Trifernal(copyright) (3-phenylbutanal; origin: Firmenich SA, Geneva, Switzerland) and xcex1-sinensal.
Non-limiting examples for ketones which can be released from the xcex1-keto esters include camphor, carvone, menthone, ionones, irones, damascenones and damacones, 4-(4-hydroxy-1-phenyl)-2-butanone (raspberry ketone) and Hedione(copyright) (methyl dihydrojasmonate; origin: Firmenich SA, Geneva, Switzerland).
With respect to the fragrant compounds carrying an olefin group, in principle any compound containing such olefin group and, in addition, any osmophoric group known in perfumery can be used. As non-limiting examples for osmophoric groups, one can cite alcohol, ether, ester, aldehyde and keto groups, the thio analogues of the said groups, nitrile, nitro and olefin groups.
As non-limiting examples for fragrant compounds which carry an olefin group, there can be cited linalool, 1,3,5-undecatrienes, myrcene, myrcenol, dihydromyrcenol, nerolidol, sinensals, limonene, carvone and farnesenes.
It is quite obvious, however, that the invention is perfectly general and can relate to many other aldehydes, ketones and olefins which are useful as fragrant compounds. The person skilled in the art is quite able to choose these compounds from the general knowledge in the art and from the olfactive effect it is desired to achieve. The above list is therefore more illustrative for the compounds which are known to a person skilled in the art, and whose delivery can be improved. It is clearly quite impossible to cite in an exhaustive manner all aldehydes, ketones and olefins which have a pleasant odor and which can be used in the form of derivatives in the xcex1-keto esters of formula (III) from which they are released upon exposure to light.
The xcex1-keto esters of the present invention are in particular appropriate for delivering fragrant aldehydes and ketones and fragrant compounds containing an olefin group which are very volatile or which have a low perception threshold. Preferred aldehydes and ketones include citronellal, citral, hydroxycitronellal, Hedione(copyright), raspberry ketone and aldehydes from C6 to C13, saturated or unsaturated. Preferred fragrant compound containing an olefin group include linalool, myrcene and myrcenol.
In case the xcex1-keto esters of the present invention are used to release exclusively aldehydes or ketones, the group Rxe2x80x2* is hydrogen, phenyl, cyclohexyl or cyclopentyl, methyl, ethyl, n-propyl, isopropyl, sec-butyl, isobutyl or tert-butyl, i.e. groups which do not provide an abstractable hydrogen atom in xcex3-position to the xcex1-keto function or which do not form a stable radical when a hydrogen radical is abstracted from them. In the latter case, small amounts of olefin may be formed which however do not interfere with the aldehyde or ketone released.
Likewise, when the xcex1-keto esters of the present invention are used to release a fragrant compound containing an olefin group only, then the group Rxe2x80x3* will be hydrogen or a methyl, ethyl or tert-butyl group, thus a group which does not provide an abstractable proton in xcex3-position to the xcex1-keto function or which do not form a stable radical when a hydrogen radical is abstracted from them.
It is preferred when the fragrance delivery system of the present invention contains xcex1-keto esters of formula (III) in which Rxe2x80x3* is the organic part of a primary or secondary alcohol from which is derived a fragrant aldehyde or ketone and in which Rxe2x80x2* is phenyl, cyclohexyl or an alkyl group from C1 to C4.
As is clear from the above, the xcex1-keto esters of formula (III) always react, before releasing a fragrant compound, in an intramolecular hydrogen abstraction reaction. A fragrance delivery system containing the xcex1-keto esters of formula (III) therefore in no case needs an external hydrogen radical source, contrary to the 2-benzoyl and 2-alkanoyl benzoates of formulae (I) and (II) from which some compounds react under abstraction of a hydrogen radical from the solvent. A fragrance delivery system containing xcex1-keto esters of the present invention may thus comprise a solvent the choice of which is not supposed to be critical. Suitable classes of solvents include alcohols, ethers, esters, ketones, amines and aminoalcohols.
The xcex1-keto esters of formula (III) can be prepared, on one hand, by esterification of the respective xcex1-ketoacids with the primary or secondary alcohols which are the precursors of the fragrant aldehydes and ketones to be releasead. Another way for the preparation of the xcex1-keto esters of the present invention is the reaction of the bis(oxalyl) ester of the primary or secondary precursor alcohol Rxe2x80x3*OH with the Grignard compound of the appropriate group Rxe2x80x2* as defined in formula(III). The reaction is illustrated in the scheme below. 
The bis(oxalyl) ester is prepared from oxalyl chloride and the desired alcohol, see Syn. Commun. 1981, 943.
Various xcex1-keto esters of formula (III) in which Rxe2x80x2* is phenyl and Rxe2x80x3* is the alcohol precursor of a fragrant aldehyde are described in the literature. Also described is hexyl (cyclohexyl)oxoacetate (see DE-OS 29 09 951 to Bayer AG, describing the use of the said compound as starting product for the synthesis of catalysts for the polymerisation of olefins), which would release n-hexanal upon irridiation.
The release of the above-mentioned fragrant compounds from the delivery system occurs upon the exposure to light, e.g. the normal daylight which can penetrate through ordinary windows in houses and which is not particularly rich in UV-radiation. It goes without saying that upon exposure to bright sunlight, in particular outdoors, the release of the fragrant alcohol, aldehyde, ketone or alkene will occur faster and to a greater extent than upon exposure to the light in a room inside a building. Of course, the reaction which releases the fragrant compound from the delivery system can also be initiated by an appropriate artificial lamp.
The fragrance delivery systems of the present invention can be used in any application in which a prolonged, defined release of the above-mentioned fragrant compounds is desired. They therefore mostly find use in functional perfumery, in articles which are exposed to daylight when in use or which are applied to other articles which thereafter are exposed to daylight. Suitable examples include air-fresheners in liquid and solid form which, with the delivery system of the present invention, still can release a fragrance when conventional air-fresheners, i.e. those not containing the system of the present invention, are exhausted. Other examples are window and household cleaners, all purpose-cleaners and furniture polish. The surfaces which have been cleaned with such cleaners will diffuse the smell of the perfume much longer than when cleaned with conventional cleaners. Detergents and fabric softeners can also contain the delivery system of the present invention, and the clothes washed or treated with such detergents or softeners will diffuse the fragrant compound even after having been stored in the wardrobe for weeks or months.
The release of the fragrant compound occurs in all the above-mentioned application examples. All possible types of window, household, all-purpose cleaners, air-fresheners, detergents and fabric softeners can be used with the fragrance delivery system of the present invention, which has revealed itself to be useful in all types of these above-mentioned application examples.
It can be said that generally all products which can be applied to a surface which is exposable to light may contain the system of the present invention. Examples include surfaces which belong to the human body, like skin or hair, surfaces in buildings and apartments, like floors, windows, tiles or furniture, or surfaces of clothes. It is clear that the system of the invention can also be used to release fragrances from liquids, like in liquid air-fresheners. The possible applications of this type, however, appear to be less general than the application on the various surfaces mentioned.
Of course, the above examples are only illustrative and non-limiting as referring to preferred embodiments. All other current articles in functional and fine perfumery may contain the system of the present invention, and these articles include soaps, bath or shower gels, shampoos, hairsprays or other hair care products, cosmetic preparations, body deodorants, and even perfumes or colognes.
In the above-cited applications, the device of the present invention can be used alone or with other perfuming ingredients, solvents and adjuvants of current use in the art. The nature and variety of these co-ingredients does not require a detailed description which, moreover could not be exhaustive, and a person skilled in the art will be able to choose said coingredients by his general knowledge and in function of the nature of the product to be perfumed and the olfactive effect sought. These perfuming ingredients belong to such varied chemical classes as alcohols, aldehydes, ketones, esters, ethers, acetates, nitrites, terpene hydrocarbons, nitrogen- or sulfur-containing heterocyclic compounds, as well as essential oils of natural or synthetic origin. By way of example, embodiments of compounds can be found in standard reference works, such as the book of S. Arctander, Perfume and Flavor Chemicals, 1969, Montclair, N.J., USA, or more recent versions thereof, or in other works of similar nature.
The proportions in which the system of the present invention can be incorporated in the various above-mentioned products vary within a wide range of values. These values depend on the nature of the fragrant compound to be released, the nature of the article or product which is to be perfumed and the desired olfactive effect, as well as on the nature of the co-ingredients in a given composition when the system of the present invention is used in admixture with perfuming co-ingredients, solvents or adjuvants of current use in the art.
By way of example, one can cite typical concentrations of the order of 0.01 to 5%, or even 10% by weight relative to the weight of the consumer products cited above into which it is incorporated. Higher concentrations than those mentioned above can be used when the system is applied in perfuming compositions, perfumes or colognes.